Current generation single in-line memory modules (SIMMs) for certain brands of computers use eight one-megabit (1M) dynamic random access memories (DRAMs) arranged in a x1 configuration (having one data out signal), which supplies the computer with one megabyte (MB) of memory. Since the DRAMs are arranged in a x1 configuration, one data bit can be extracted from each chip at a time. When a module with eight 1Mx1 DRAMs is installed in a computer capable of handling eight bits of data at a time (i.e. an 8-bit computer), it accesses one bit location from each of eight DRAMs on a module simultaneously, thereby receiving the eight bits of data it is capable of handling. In 16-bit computers, modules containing eight 1Mx1 DRAMs are installed in groups of two in the computer. To obtain the 16 bits of data the computer is capable of handling, all 16 DRAMs are accessed simultaneously, and the computer receives one bit of data from each DRAM for a total of 16 data bits. Each time a 1Mx1 DRAM is accessed, it requires about 80 mA of current to be supplied. To access the 16 DRAMs simultaneously requires approximately 640 mA of current per module, or 1,280 mA total.
Some SIMMs use 1Mx4 DRAMs, with each DRAM having four bits of data. A module using two 1Mx4 chips supplies 1MB of memory, as does a module using eight 1Mx1 chips. A module with two 1Mx4 devices is functionally equivalent to a module using eight 1Mx1 devices, but has fewer parts, thereby being easier to assemble and somewhat more reliable due to fewer solder joints. There is not much power savings using a module with two 1Mx4 DRAMs over a module using eight 1Mx1 DRAMs, as all the devices on either module are turned on each time one of the devices is accessed in order to access eight data bits, and to access two 1Mx4 DRAMs requires about as much power as accessing eight 1Mx1 DRAMs.
In most computers, addressed words are an even number of bits, such as eight, sixteen or thirty-two bits. This fits neatly into memory array blocks which use x4 chips. This convenient arrangement is complicated by the fact that a system of memory parity has proven to be very effective in error detection. The parity is an additional bit for each word, so that an eight bit word ("byte") is addressed as nine bits, the ninth bit being parity.
Reducing power consumption in a computer or other electronic device is a design goal, as overtaxing a computer's power supply is a common concern. With the addition of modem cards, memory boards, graphics cards, hard disk controller cards, printer buffer cards, and mouse cards, the chances of burning out the computer's power supply from drawing too much current becomes a possibility. Even if the power supply is not unduly stressed, a component which uses more power than a similar component will release more heat, thereby increasing the temperature of the component as well as the inside of the computer or electronic device. Elevated temperatures within the component or within the chassis of a computer can cause other components in the computer to operate more slowly or to fail prematurely.
Reducing the amount of current used by the components in a computer is also a concern to designers of portable computers. The length of time between battery recharges for various brands and types of computers ranges from about two hours to 12 hours. Reducing the amount of current the computer uses, thereby extending the length of time the computer can be run off the battery, is a design concern as well as a marketing concern.
For the reasons listed above, reducing the power consumption of components installed in a computer is a goal of computer component designers and computer manufacturers.